The patient lost more than 120kg during this controlled fast. He was then able to mantain his normal weight and suffered no ill-effects.

Ketosis and medicine

There is plenty of russian and romanian literature on the subject of therapeutic fasting.

Little can be found translated to english, but examples include the over 6000 patients cured through fasting since 1972 by Dr. Yuri Nikolaev, director of the fasting clinic of the Moscow Research Institute of Psychiatry and co-author of the book Голодание ради здоровья ("Fasting for Health", ISBN 5-268-00434-4).

Just as there are many remote causes of plague, heat, insects, rats, but only one common cause, the plague bacillus, there are a great many remote causes of cancer-tar, rays, arsenic, pressure, urethane- but there is only one common cause into which all other causes of cancer merge, the irreversible injuring of respiration.

If the cells in your body cannot breathe, they need to switch to another form of energy in order to stay alive.

They start to ferment, a way to produce energy that has been used by organisms even before oxygen became an available resource on Earth.

What fuels the fermentation process is glucose, and that is why ketogenic diets can be effective in the management of cancer and make it curable without aggressive medicine.

Intermittent fasting

These new scientific results helped shaping multiple approaches to what is now known as intermittent fasting. Most of these diets advocate eating a <500kcal meal 2/3 days a week, and binge-eating for the rest of the week.

A supporter of this approach is mathematician and author Nassim Taleb.

In Taleb's Fasting, Relative Frequencies paper is illustrated a way to imitate naturally-occurring famine periods following a better (non-gaussian) mathematical model, on a week but also months and years base.

I have no idea of how much much weight I lost during that trip, but comparing of the few pictures I took I can see how my body changed:

MIGHTY MORPHING POWER HUNGERS

The changes that I have noticed were mainly:

faster distances covered

increased stamina

loss of fat tissue

bigger muscles in the tights and leg area

numbness in the joints of the hand (swollend hands because constantly pointing down as I walked, fixed by using a walking stick)

small dents in my fingernails (lack of calcium or other minerals, fixed by drinking yogurt)

more focused and relaxed mind

better sex

solid sleeping pattern that follows daylight cycles, to the point that it almost fixed my inverted circadian rythm

less or no hunger in-between meals, hungry like a wolf at the table

Starving yourself makes you fat

Modern age brought people to depend on a defined set of patterns that regulate income, time to dedicate to one's leisure and personal growth, meals, energy needs.

In the West we currently take 3 daily meals + snacks as granted, but as a species we have been able to survive well before the work/produce/consume/die cycle was ingrained in our society.

Even if we are advancing as a civilization and food is always available, our body and the primitive part of our brain still reason in terms of randomness and scaricity of resources.

This is why, I believe, you tend to get fatter after a period of starvation:

the brain notices you are ignoring hunger waves

it assumes you are experiencing lack of available preys or fruit trees in your area

body system goes in stand-by mode to save resources and deal with excess materials

as soon as you ingest something the brain commands you to eat more and pack up fat, wondering if you're ever going to find another prey or berry bush

you become a fat catlady

So, don't be stupid, if you want to lose weight start eating smart and often.

Too much of too good stuff is going to kill you and that's probably why we have diabetes, cancer and other kind of illness. Most ancient religions advocate weekly or monthly fasting, along with keeping the population humble it helped keeping it in good health.

Conclusion

From this collection of articles and my personal experience I can conclude that our body can survive long periods of little or no provisions, as long as you listen to what your body tells you and adapt as you go.